1. Field of the Invention
This invention relates to thermosetting resin compositions for overcoats of flexible circuits, which are excellent in low shrinkage during curing and flexibility, and particularly in that the resulting overcoats are difficult to deteriorate in qualities, e.g., to overharden, to increase in curling, and the like, even after being allowed to stand for a long time at elevated temperatures. It relates also to a film carrier coated with an overcoat agent comprising, as the main ingredient, such a resin composition for overcoat of flexible circuit, as well as to a film device where such film carrier is used.
2. Prior Art
The surface protective films of flexible wiring circuits have heretofore been formed, e.g., by cutting polyimide films, called as coverlay films, using a die made corresponding to the pattern, which are then adhered onto a substrate with an adhesive, or by applying a ultraviolet rays- curable or thermosetting overcoat composition the film from which is imparted with flexibility, according to the screen printing method, followed by curing. However, the coverlay film method is undesirable in workability, and the method where an overcoat agent is used is unsatisfying in curling upon curing and also in flexibility, and there have been known no methods of forming surface protective films for flexible wiring circuits which can meet the required performances.
On the other hand, recently, the so-called TAB method has got increasingly employed where film carriers which are, as an IC package for liquid-crystals driving, suitable for high-densifying or thinning. The basic structure of a film carrier is mainly composed of heat-resistant, insulating film base such as polyimide or the like, and an electrical conductor such as copper foil or the like, glued onto the film base through an adhesive layer composed mainly of an epoxy resin as the main ingredient, the wiring pattern having been formed on the copper foil by etching. And, a film carrier device is made by connecting an IC to such tape carrier followed by confining with the use of a confining resin. To prevent the reliability from being decreased due to pattern shortening, erosion, migration, whisker occurrence, or the like, a surface protective film is usually formed on such film carrier, using an overcoat agent. As such overcoat agent for film carriers, an epoxy-based one and a polyimide-based one are used. However, the former has not been satisfactory in curling during curing and flexibility of the coat film formed, and the latter has not been satisfactory in adhesiveness to the IC confining resin, workability or the like. For these reasons, at present, two or more different overcoat agents are concurrently used to compensate each other (See Japanese patent application laid-open (kokai) No. 283,575/""94) .
On the other hand, the present inventor had studied intensively to solve the above problems, and, as the results, found that curable resin compositions having properties required, e.g., of overcoats for flexible circuit, such as low shrinkage during curing, and whose cured products have satisfactory properties such as flexibility, adherence, electrical insulation, chemical resistance, heat resistance, etc., can be prepared by mixing a polyol with a number-average molecular weight of 1,000-8,000 and having 2-10 hydroxyl groups per molecule, or a polyol with a number-average molecular weight of 200-600 and having 2-10 hydroxyl groups per molecule, with a polyol with a number-average molecular weight of 13,000-30,000 and having 2-10 hydroxyl groups per molecule, and a polyblock isocyanate, and that, inter alia, a polyol or a polyblock isocyanate each having a polybutadiene skeleton is effective in providing flexibility and low shrinkage during curing. See Japanese patent applications Nos. 219,610/""97 and 219,611/""97.
An overcoat formed by using a resin composition comprising an ingredient with a polybutadiene skeleton is, however, apt to be oxidized, and therefore, undergo such changes that the coat film gets overhardened and the curling is increased, when it is left, e.g., in an elevated-temperature environment.
In particular, if such resin composition is used as an overcoating agent for printed circuit bases such as flexible circuit, there may be involved such trouble that the coat film gets overhardened and the curling is increased, because such printed circuit bases are made to pass, during their production process, through more than 150xc2x0 C. environment, several times or for a long time.
Problems to be Solved by the Invention
It is an object of the present invention to provide an overcaoting agent which can give a coat film involving no such trouble that the coat film gets overhardened and the curling is increased. Other objects will be apparent from what will be described below.
Means for solving the problems
The present inventor has studied intensively to solve the above problems, and as the results, found that the use of a resin whose double bonds in the polybutadiene skeleton, have been added with hydrogen atoms, i.e., a resin which has a hydrogenated polybutadiene skeleton, can avoid the above-mentioned trouble. The present invention has been completed on the basis of these findings.
Accordingly, the present invention relates to:
1. A curable resin composition for overcoat of flexible circuit which comprises a hydrogenated polybutadiene polyol with a number-average molecular weight of 1,000-8,000 and having 2-10 hydroxyl groups per molecule (Polyol A), and a polybutadiene polyblock isocyanate (Isocyanate X);
2. A curable resin composition for overcoat of flexible circuit which comprises a hydrogenated polybutadiene polyol with a number-average molecular weight of 1,000-8,000 and having 2-10 hydroxyl groups per molecule (Polyol A), and a hydrogenated polybutadiene polyblock isocyanate with a number-average molecular weight of 1,000-8,000 and having 2-10 blockisocyanate groups per molecule (Isocyanate Xa), said hydrogenated polybutadiene polyblock isocyanate (Isocyanate Xa) being in an amount of 0.8-3.5 gram equivalents based on (i.e., per) one gram equivalent of the total hydroxyl groups of said Polyol A;
3. A curable resin composition for overcoat of flexible circuit which comprises a hydrogenated polybutadiene polyol with a number-average molecular weight of 1,000-8,000 and having 2-10 hydroxyl groups per molecule (Polyol A), a hydrogenated polybutadiene polyblock isocyanate with a number-average molecular weight of 1,000-8,000 and having 2-10 blockisocyanate groups per molecule (Isocyanate Xa), and a hydrogenated polybutadiene polyol with a number-average molecular weight of 13,000-30,000 and having 2-10 hydroxyl groups per molecule (Polyol B), wherein the weight ratio (as solid content) of said two polyols is (Polyol A):(Polyol B)=40:60-90:10, and said polyblock isocyanate (Isocyanate Xa) is in an amount of 0.8-3.5 gram equivalents based on, i.e., per one gram equivalent of, the total hydroxyl groups of the two polyols (Polyol A plus Polyol B);
4. A curable resin composition for overcoat of flexible circuit which comprises a polyol with a number-average molecular weight of 200-600 and having 2-10 hydroxyl groups per molecule (Polyol C), a hydrogenated polybutadiene polyblock isocyanate with a number-average molecular weight of 1,000-8,000 and having 2-10 blockisocyanate groups per molecule (Isocyanate Xa), and a hydrogenated polybutadiene polyol with a number-average molecular weight of 13,000-30,000 and having 2-10 hydroxyl groups per molecule (Polyol B), wherein the weight ratio (as solid content) of the two polyols is (Polyol C):(Polyol B)=20:80-50:50 and said polyblock isocyanate (Isocyanate Xa) is in an amount of 0.8-3.5 gram equivalents based on one gram equivalent of the total hydroxyl groups of the polyols;
5. The curable resin composition for overcoat of flexible circuit as set forth above which further comprises fine rubber particles and/or fine polyamide particles;
6. A film carrier coated on the circuit pattern surface side, with an overcoat agent comprising, as the main ingredient, a curable resin composition for overcoat of flexible circuit as set forth above; and
7. A film carrier device which comprises the film carrier as set forth above.
A hydrogenated polybutadiene polyol with a number-average molecular weight of 1,000-8,000 and having 2-10 hydroxyl groups per molecule (Polyol A) is important to impart properties to cured products, for example, those observed for resins having a higher crosslinking density such as heat resistance, chemical resistance, and the like, as well as those observed for resins having a lower crosslinking density such as flexibility, low shrinkage, and the like, in the way where the two kinds of properties are well balanced. If the molecular weight is below this range or if the number of hydroxyl groups per molecule exceeds this range, the crosslinking density upon curing becomes higher, providing harder cured products and insufficient properties for low shrinkage upon curing and flexibility of a cured film. On the other hand, if the molecular weight exceeds said range or if the number of hydroxyl groups per molecule is below said range, the crosslinking density upon curing becomes lower, providing more flexible cured products while significantly deteriorating heat resistance and chemical resistance of the cured film.
A hydrogenated polybutadiene polyblock isosyanate with a number-average molecular weight of 1,000-8,000 and having 2-10 blockisocyanate groups per molecule (Isocyanate Xa) is, like Polyol A, important to impart properties to cured products, for example, those observed for resins having a higher crosslinking density such as heat resistance, chemical resistance, and the like, as well as those observed for resins having a lower crosslinking density such as flexibility, low shrinkage, and the like, in the way where the two kinds of properties are well balanced. If the molecular weight is below this range or if the number of hydroxyl groups per molecule exceeds this range, the crosslinking density upon curing becomes higher, providing harder cured products and insufficient properties for low shrinkage upon curing and flexibility of a cured film. On the other hand, if the molecular weight exceeds said range or if the number of blockisocyanate groups per molecule is below said range, the crosslinking density upon curing becomes lower, providing more flexible cured products while significantly deteriorating heat resistance and chemical resistance of the cured film.
A hydrogenated polybutadiene polyol with a number-average molecular weight of 13,000-30,000 and having 2-10 hydroxyl groups per molecule (Polyol B) is important to decrease the crosslinking density, whereby properties such as low shrinkage upon curing and flexibility and the like of the cured products are much improved.
A polyol with a number-average molecular weigh of 200-600 and having 2-10 hydroxyl groups per molecule (Polyol C) is important to increase the crosslinking density whereby the cured products are improved in heat resistance and chemical resistance.
When a polyol (A) and a blockisocyanate (Xa) are cured together, the chemical and heat resistances of the cured products are considerably well balanced with the low shrinkage upon curing and flexibility. In order to decrease the warp or curling upon curing and the flexibility of a coat film, a polyol (B) can be added to lower the crosslinking density. In this case, the two kinds of polyols have to be used in a weight ratio (as solid content) of (Polyol A):(Polyol B)=40:60-90:10, thereby all the properties are well balanced. If Polyol B is used in an weight ratio exceeding this range, the crosslinking density is lowered excessively whereby the properties of the coat film such as heat resistance, chemical resistance and the like are remarkably deteriorated.
On the other hand, when a polyol (C) is cured with a blockisocyanate (Xa), unsatisfactory results can only be obtained, regarding the curling upon curing and the flexibility of the resulting coat film, and therefore, a polyol (B) must be used together therewith. In this case, the two kinds of polyols are preferably used in a weight ratio (as solid content) of (Polyol C):(Polyol B)=20:80-50:50, whereby all the properties are balanced. If Polyol C is used in a weight ratio smaller than this range, the crosslinking density is lowered excessively whereby the properties of the coat film such as heat resistance and chemical resistance and the like are remarkably deteriorated, while if Polyol C is used in a higher weight ratio, the crosslinking density is increased excessively whereby the low shrinkage upon curing and the flexibility of the coat film are deteriorated.
The reason why the double bonds in the butadiene skeleton have been added with hydrogen atoms with respect to a polyol (A), a polyol (B) and a polyblock isocyanate (Xa) is with the view of preventing the coat film from being hardened excessively and the curling from being increased due to the (oxidation) reaction of the double bonds at elevated temperatures.
As a hydrogenated polybutadiene polyol (A), any ploybutadiene polyol with a number-average molecular weight of 1,000-8,000 and having 2-10 hydroxyl groups per molecule, whose double bonds in the butadiene skeleton have been added with hydrogen atoms (i.e., hydrogenated) may be used. Examples thereof include commercially available xe2x80x9cGI-1000xe2x80x9d and xe2x80x9cGI-3000xe2x80x9d (both manufactured by Nippon Soda Co., Ltd.) and those obtainable by hydrogenating commercially available polybutadienes such as xe2x80x9cG1000xe2x80x9d and xe2x80x9cGQ1000xe2x80x9d (both manufactured by Nippon Soda Co., Ltd.) and xe2x80x9cR-45EPIxe2x80x9d (manufactured by Idemitsu Petrochemical).
As a hydrogenated polybutadiene polyblock isocyanate (Xa), any polybutadiene polyblock isocyanate with a number-average molecular weight of 1,000-8,000 and having 2-10 blockisocyanate groups per molecule, whose double bonds in the butadiene skeleton have been hydrogenated, may be used. Examples thereof include those obtainable by blocking, with a blocking agent, a commercially available polybutadiene polyisocyanete such as xe2x80x9cTP1002xe2x80x9d (manufactured by Nippon Soda Co., Ltd.) or xe2x80x9cHTP-9xe2x80x9d (manufactured by Idemitsu Petrochemical), followed by hydrogenating, and those obtainable by reacting a commercially available OH-terminated hydrogenated polybutadiene such as xe2x80x9cGI-1000xe2x80x9d or xe2x80x9cGI-3000xe2x80x9d (both manufactured by Nippon Soda Co., Ltd.) with a diisocyanate in an amount of two gram equivalents per one gram equivalent of the hydroxyl groups in the OH-terminated polybutadiene to obtain the corresponding isocyanate-terminated compound, followed by blocking with a blocking agent. Such blocking agents include, for example, a compound having only one active hydrogen atom which can react with an isocyanate group, per molecule and preferably dissociates again at a temperature below 170xc2x0 C. after reaction with the isocyanate group, and include, for example, xcex5-caprolactam, diethyl malonate, ethyl acetoacetate, acetoxime, methylethylketoxime, phenol, cresol, etc.
As a hydrogenated polybutadiene polyol (B), any polyol with a number-average molecular weight of 13,000-30,000 and having 2-10 hydroxyl groups per molecule, whose double bonds in the butadiene skeleton have been hydrogenated, may be used. Examples thereof include those obtainable by reactimg a hydrogenated polybutadiene polyol having a molecular weight of about 1,000-3,000 such as xe2x80x9cGI-1000xe2x80x9d or xe2x80x9cGI-3000xe2x80x9d (both manufactured by Nippon Soda Co.,Ltd.) with a diisocyanate whereby the hydrogenated polybutadiene polyol is increased in moleculer weight to a range of about 13,000-30,000, or those obtainable by reacting a polybutadiene polyol such as xe2x80x9cG1000xe2x80x9d (manufactured by Nippon Soda Co.,Ltd.) or xe2x80x9cR-45EPIxe2x80x9d (manufactured by Idemitsu Petrochemical) with a diisocyanate whereby the polybutadiene polyol is increased in molecular weight to a range of about 13,000-30,000, followed by hydrogenating.
As a polyol (C), any polyol with a number-average molecular weight of 200-600 and having 2-10 hydroxyl groups per molecule may be used, irresoective of the resin structure. For example, EO denatured pentaerythritol, xe2x80x9cPE555xe2x80x9d (manufactured by Toho Chemical Industries Co., Ltd.), EO denatured trimethyrol propane, xe2x80x9cTP880xe2x80x9d (manufactured by Toho Chemical Industries Co., Ltd.), and polycaprolactone triol, xe2x80x9cPrakcel 303xe2x80x9d, and xe2x80x9cPrakcel 305xe2x80x9d (manufactured by Dicel Huls).
Moreover, the composition of the present invention may optionally comprise a curing accelerator for polyol and isocyanate, a filler, an additive, a thixotropic agent, a solvent and the like as optional components, in addition to the above essential components. Particularly, in order to improve bending resistance, fine rubber particles may be preferably added. Moreover, fine polyamide particles may be added to further improve adherence to a base copper circuit, a base material such as a polyimide or polyester film, an adhesive layer, etc.
Such fine rubber particles include, for example, any fine particles of resins exhibiting rubber elasticity such as acrylonitrile butadiene rubber, butadiene rubber, acryl rubber, which have been subjected to chemical crosslinking treatment to make insoluble in an organic solvent and infusible. For example, xe2x80x9cXER-91xe2x80x9d (manufactured by Japan Synthetic Rubber Co., Ltd.), xe2x80x9cStaphyloide AC3355xe2x80x9d, xe2x80x9cStaphyloide AC3832xe2x80x9d and xe2x80x9cIM101xe2x80x9d (manufactured by Takeda Chemical Industries, Ltd.), xe2x80x9cParaloide EXL2655xe2x80x9d and xe2x80x9cParaloide EXL2602xe2x80x9d (manufactured by Kureha Chemical Industries, Co., Ltd.) are encompassed.
Fine polyamide particles include any fine particles of 50 micron or smaller consisting of resin having amide linkages, for example, fatty polyamides such as nylon, aromatic polyamides such as Kevlar, and polyamidoimides. For example, xe2x80x9cVESTOSINT 2070xe2x80x9d (manufactured by Daicel Huls) and xe2x80x9cSP500xe2x80x9d (manufactured by Toray Industries, Inc.) may be mentioned.
The method of curing the present curable resin composition in itself is not particularly limited, but carried out according to the conventional methods.